This paper discusses the distinctive nature of longitudinal data and the types of policy and research questions they can address. The paper provides an overview of the Longitudinal Surveys of Australian Youth (LSAY) program, and how it compares with longitudinal surveys in other OECD countries. The LSAY program, which is operated by ACER with support from DETYA and all school authorities in Australia, has now accumulated 20 years of data on cohorts of young Australians as they move through education and training and into the labour market. The LSAY surveys probably collect more extensive information on young Australians' educational and labour market experiences than is available from any other single source. The LSAY data are publicly available for use by the research community, and the paper concludes by indicating how the database and key results can be accessed.